Derechos, Droughts, Hottest July on Record, Shattered
High Temp Records, Greenland Ice Sheet Melts.Just what is going on with the weather these
days?Is this weather really abnormal or
does it just seem to be that way? Is this part of a trend?Does global climate change mean we’ll have
more of these extreme weather events?Being
a data and analytics person, I started looking to see what data analysis had
been done on this subject.

The US Climate Extremes Index[i] provides
a measure to track the occurrence of extreme data (although it doesn’t take
into account Derechos and other severe wind events).The trend of the index (smoothed) has been on
the rise since 1970 and now is at an all time high, as shown below. The Index
was at a record high 46% during the January-July period, over twice the average
value, and surpassing the previous record large CEI of 42% percent which
occurred in 1934.Extremes in warm
daytime temperatures (83 percent) and warm nighttime temperatures (74 percent)
both covered record large areas of the nation, contributing to the record high
year-to-date USCEI value.

This index is
compiled by combining measurements throughout the country (1,218-station US Historical Climatology Network)
that show the percentage of the country impacted by extreme weather in terms of
maximum temperatures much above or below normal, minimum temperatures
above/below normal, percentage of country in severe drought/severe moisture
surplus, percentage of the country with a much greater than normal proportion
of precipitation derived from extreme 1 day events, and the percentage of the
country with a much greater than normal number of days with
precipitation/without precipitation.

The U.S. Global
Change Research Program in 2009 published a study which documented the changing
climate and its impact on the United
States[ii]. The
study uses 3 standard forms of data analysis: 1) reports on observations, 2)
predictions based on the observed trends, and 3) modeling to better predict future
climate changes based on various assumptions about the amount of heat-trapping
gases in the atmosphere.While the first
two types are based on large quantities of collected data, they use only U.S.
observations.The modeling, however,
must be done on a global basis which substantially increases the amount of data
that must be crunched.

Here are some of the findings as they relate to extreme
weather:

Overall Warming of the Climate

Temperatures, on average, in the1993-2008 period are 1-2ºF
higher than in the 1961-79 baseline.By
the end of the century, the average U.S. temperature is projected to
increase by approximately 7-11ºF under a high emissions model and by
approximately 4-6.5ºF under a lower emissions scenario. The temperature observations show that there
has been an increase in warmer and more frequent warm days and warm nights, and
warmer and less frequent cold days and cold nights in most areas.

More intense, more frequent, and longer-lasting heat waves

In the past several decades, there has been an increasing
trend in high-humidity heat waves, characterized by extremely high nighttime
temperatures.Parts of the South that
currently have about 60 days per year with temperatures over 90ºF are projected
to experience 150 or more days a year above 90ºF under a higher emissions
scenario.In addition to occurring more
frequently, at the end of this century these very hot days are projected to be
about 10ºF hotter than they are today.

Increased extremes of summer dryness and winter wetness with a generally
greater risk of droughts and floods.

Trends in drought have strong regional variations.Over the past 50 years, with increasing
temperatures, the frequency of drought in many parts of the West and Southeast
has increased significantly.Models show
that the Southwest, in particular, is expected to experience increasing drought
as the dry zone just outside of the tropics expands northward with global
warming.

Precipitation coming in heavier downpours, with longer dry periods in
between

While average precipitation over
the nation as a whole increased by about 7% over the past century, the amount
of precipitation falling in the heaviest 1% of rain events increased nearly
20%.One of the outputs of the climate
modeling is to project the probability of certain events. For example, heavy downpours that are now a “1
in 20 year occurrence” are projected to occur about “once every 4-15 years” by
the end of the century.These heavy downpours are expected to be
10-25% heavier by the end of the century than they are now. This will likely cause more flooding events
(flooding depends both upon the weather and the susceptibility of the area to
being flooded).

More intense but fewer severe storms

Reports of severe weather such as
tornadoes and severe thunderstorms have increased during the past 50 years.
However the climate study indicates that much of this may be due to better
monitoring technologies, changes in population areas, and increasing public
awareness. Climate models do project an increase in the frequency of
environmental conditions favorable to severe thunderstorms.But the report notes, “the inability to
adequately model the small-scale conditions involved in thunderstorm
development remains a limiting factor in projecting the future character of
severe thunderstorms and other small-scale weather phenomena.[iii]”Advances in modeling and big data analytics,
as well as improved monitoring networks are likely to reduce this limitation in
the future.

The June Derecho that hit the Washington metropolitan
area shows an example of the current state of the art in forecasting a severe
storm.The Storm Prediction Center of
NOAA was able to provide approximately 4 hours advance warning of the
storm.Longer term predictions would
require additional data about the atmospheric instability that propelled the
Derecho from Iowa to the Washington
Metro area, as well as better real time modeling.

Shift of storm tracks towards the poles

Cold season storm tracks are
shifting northward over the last 50 years, with a decrease in the frequency of
storms in mid-latitude areas.The
northward shift is projected to continue, and strong cold season storms are
likely to become stronger and more frequent, with greater wind speeds and more
extreme wave heights.

The climate changes will have an
interesting effect on the so called “lake-effect”.Over the past 50 years, there is a record of
increased lake-effect snowfall near the Great Lakes.As the climate has warmed there is less ice
on the Great Lakes which has allowed greater
evaporation from the surface resulting in heavier snowstorms.Eventually, the temperatures are expected to
rise sufficiently that much of the precipitation will end up falling as rain,
reducing the snow totals.

Mutual Interactions

While trending of individual elements such as temperatures
is useful, accurate predictions require consideration of the interaction
between the climate elements.For
example, there is mutual enhancement effect between droughts and heat
waves.Heat waves enhance soil drying,
and drier soil heats the air above more since no energy goes into evaporating
the soil moisture.Big data modeling can
show the results of this escalating cycle of warming on the future climate.

The New Normal

So it seems that all this abnormal weather we are seeing
will become the new normal.Forewarned
is forearmed!